they're used in cardiac muscle fibers during depolarization; they open quickly and remain open for only a few milliseconds

what is a plateau and why does it occur?

-it is a time of maintained depolarization
-occurs when influx=efflux:
Opening of K+ channels begins (efflux) and opening of Ca+ channels in sarcolemma (influx)

what happens during the plateau of a cardiac muscle cell?

transmembrane remains near 0; once approaches +3-mV, the sodium channels close and the cell begins to pump Na+ out of the cell. as they close, calcium gated channels are opening and the entry of Ca2+ balances the loss of Na+ and the membrane hovers near 0mV

what two things happen once the Ca2+ ions are released during the plateau period?

1. the calcium triggers the calcium release from the SR due to the influx of calcium from interstitial fluid
2. contraction is triggered

what are slow calcium channels?

theyre involved in the plateau period of cardiac fiber; they open slowly and remain open for a long period of time and are present when K+ channels open and close

explain the contraction state of a cardiac muscle fiber compared to a skeletal.

-its 0.25 seconds compared to .001 seconds in skeletal; its a much longer contraction state

what is a benefit of the 0.25 seconds contraction state compared to .001?

it prevents early repolarization and the refractory period lasts longer

is the depolarization faster or slower in a cardiac muscle fiber than a skeletal?

faster

what happens during repolarization of a cardiac fiber?

potassium channels open, K+ ions rush out of the cell and repolarization occurs

why is the repolarization of cardiac fiber rapid?

because the Ca2++ close and increase the permeability

what is the diameter of a smooth muscle fuber?

5-10um

what is the length of a smooth muscle fiber?

30-200um

how many nuclei are in a smooth muscle?

1

what is the ratio of thick:thin filaments?

1:10-1:15

why are there no striations in smooth muscle?

because there are no sarcomeres so there are no myofibrils

what are the three characteristics of thin and thick filaments in a smooth muscle fiber?

1. no sarcomeres; no myofibrils; no striations
2. myosin heads along entire thick filament length
3. arranged diagonally so contract is in a twist

what are three characteristics of the intermediate filaments of a smooth muscle?